Cleft lip with or without cleft palate (CL/P) is a common birth defect. Previous studies have indicated that CL/P is a complex trait that is caused by a combination of genetic and environmental factors. This complexity has limited studies, such that disease mutations have only been identified in one unique family. It is also unlikely that all disease loci have been identified. The overall objective of this project is to identify disease genes involved in nonsyndromic CL/P by applying new multistaged linkage and linkage disequilibrium (LD) strategies to affected relative pairs and extended pedigrees. This multistage approach, which has not yet been applied to CL/P, is very powerful in that no prior knowledge about the involved genetic or biological processes is needed. Hypotheses to be tested: Nonsyndromic CL/P is caused by Genetic Variants at one or more loci. To test this hypothesis, CL/P families with both multiple affected members and mother/father and affected child trios will be recruited from a variety of clinical centers including: Columbus, OH; Medellin, Colombia SA; Seattle, WA; Pittsburgh; and Finland as well as smaller centers including Cleveland (Dr. Nat Robin); San Francisco (Dr. Ed Lammer) and San Diego (Dr. Marilyn Jones). The multiplex families will be the basis for initially evaluating candidate genes to test the above hypothesis using the genetic tools of linkage and linkage disequilibrium to reject (exclude) or provide evidence for support (i.e. linkage) the hypotheses. A 10 cM genome-wide screen will also be performed to find additional loci. Positive loci will be further evaluated by a combination of multipoint, multi-locus and TDT/association analyses using more densely spaced markers. The heritage of the Colombia and Finland populations have led to unique population structures that are advantageous for finding disease genes for complex traits. Comparison of these populations to the outbred US population will provide important information regarding the genetic diversity leading to CL/P. The power initially (will be sufficient to identify loci of moderate or major risk (relative risks greater than 2.0) and during the project, power will increase to be able to identify minor loci (relative risks greater than 1.5). It will be through multi- center projects such as this one, in which worldwide collaborations have been established to apply a combination of complimentary genetic strategies, that disease loci for CL/P will be identified. Ultimately, this will further the understanding of normal and abnormal craniofacial development, such that therapies to prevent CL/P can be developed and implemented.